Cellular communication systems continue to grow in popularity and have become an integral part of both personal and business communications. Cellular telephones allow users to place and receive phone calls most anywhere they travel. Moreover, as cellular telephone technology is increased, so too has the functionality of cellular devices. For example, many cellular devices now incorporate Personal Digital Assistant (PDA) features such as calendars, address books, task lists, calculators, memo and writing programs, etc. These multi-function devices usually allow users to wirelessly send and receive electronic mail (email) messages and access the internet via a cellular network and/or a wireless local area network (WLAN), for example.
As the functionality of cellular communications devices continues to increase, so too does demand for smaller devices that are easier and more convenient for users to carry. As many circuit boards and electronic components thereon are reduced in size and placed closer together, including antenna and other radio frequency (RF) components, including power amplifiers and antenna switches, various electronic components can pick up conductive energy and create interference within the system. For example, some components could pick up conducted energy directly from a power amplifier or from the radiated energy emitted by an antenna. This unwanted reception of conducted/near field radiated energy from power amplifiers and antennas may be particularly problematic in a packet burst transmission as part of a Global System for Mobile communications (GSM) system, including the 850 MHz, 900 MHz, 1800 MHz and 1900 MHz frequency bands.
Some mobile wireless communications devices have a RF metal shield, i.e. a “can,” that forms a compartment on a circuit board and receives RF circuitry therein, for example, the power amplifier and antenna switch (typically a diplexer antenna switch also termed a transmit/receiver antenna switch). One or more metallic “cans” can form radio frequency isolation compartments that may include a transceiver chip set in one “can” and the power amplifier and antenna switch in another “can” to aid RF filtering between the RF power amplifier and the antenna switch. Some signal coupling through the RF shield may be created from voltage standing waves of single or multiple harmonics, thus bypassing various components, such as filters that are formed to prevent such coupling.